The invention relates to a pre-controlled valve, in particular an electropneumatic regulating valve for an air brake system of a motor vehicle.
The electropneumatic regulating valve of the present invention comprises a valve housing, which contains an axially adjustable control piston and which can be actuated by means of at least one electromagnetic pilot valve for axial adjustment, and which is provided to actuate a valve seat assembly, which switches the compressed air flow between at least one external brake line connection, a feed pressure connection, as well as a venting port, and which comprises in essence a pot-like sealing cup with a coaxial passage, the circular ring-shaped sealing area of which corresponds with a coaxial valve seat assembly, constructed out of an external valve seat and an internal valve seat. In particular the present invention relates to a special configuration of the sealing cup.
The generic pre-controlled valve is installed inside an air brake system of a utility vehicle, for example, as an electropneumatic regulating valve, in order to correct a brake pressure in accordance with the desired braking effect. For this purpose a brake line, issuing from the regulating valve, is connected usually to a brake cylinder, which is disposed at the vehicle wheel and which produces the necessary brake force for a disk or drum brake, attached to said wheel, for the purpose of braking. The desired pressure value for the electropneumatic regulating valve can be specified both electrically and also pneumatically. However, the pneumatic drive is used only for safety in the case the electric drive fails.
One such electropneumatic regulating valve is known from the DE 196 05 562 A1. The regulating valve exhibits a control piston, which has a large area and is housed inside a valve housing and which can be moved axially over a corresponding control chamber. Opposite the control chamber, the control piston borders on a working chamber. On the side of the working chamber, a coaxial hollow pin is formed on the control piston, which serves to actuate an adjacent valve seat assembly. The valve seat assembly switches, by means of an axial adjustment of a spring-stressed sealing cup, the compressed air flow between an external brake line connection, a feed pressure connection as well as a venting port.
The control piston can be actuated by way of a pilot valve assembly with a control pressure from the side of the control chamber. The pilot valve assembly comprises here two electromagnetic pilot valves, which affect, by means of a coordinated flow around the integrated electric coils, an increase, hold, or decrease in the control pressure inside the control chamber. On the side opposite the control piston, a counterforce, resulting from the brake pressure, is effective.
The valve seat assembly, which can be actuated in such a manner by the control piston, envelops the pot-like sealing cup, which is provided with a coaxial passage, in order to lead the exhaust air, accumulated while venting the control chamber, through said passage to the venting port. The remaining circular ring-shaped sealing area of the sealing cup forms together with an opposite external valve seat, which envelops a coaxial internal valve seat, a corresponding valve seat assembly.
The compressed air of the brake line connection, connected to the working chamber, is supplied by depressing the sealing cup, whereby said sealing cup lifts off from the external valve seat so that an air flow from the feed pressure connection to the working chamber is released. A venting of the working chamber, connected to the brake line connection, is achieved by raising the internal valve seat, which is made as one piece with the control piston, with the result that the compressed air flows starting from the working chamber to the venting port.
The quality of control achieved with the prior art valve seat assembly that is described above is limited by a relatively large force component, which acts from the bottom on the sealing cup in the direction of the control piston, and which is generated in essence by the influences of the brake pressure. Opposite this bottom force component there is on the other side of the sealing cup an upper force component, which exhibits a smaller amount due to a smaller effective surface—caused by the coaxial arrangement of both valve seats—in connection with the pressure in the working chamber in the closed valve position. This imbalance of the two force components results in a relatively large hysteresis of the valve seat assembly, a feature that has a negative impact on the quality of control.
Attempts have already been made to enlarge the effective circular ring-shaped sealing area of the sealing cup by decreasing further the diameter of the piston seat. However, it has turned out that the sealing cup is stressed so unfavorably in the area of the inside rim that no reliable tightness and no exact valve function can be obtained. Enlarging the external valve seat cannot be considered because of design-related restrictions.
The sealing cup is made of an elastomer and exhibits a reinforcing insert, which is formed essentially at right angles in accordance with the cross section of the edge, whereby the horizontal leg, running below the sealing area, connects to a vertical leg, extending along an external sealing lip segment, in order to reinforce in this respect the external flank of the sealing cup. Given the edge conditions described above, this geometry does not result in an enlargement of the force component above the sealing cup. In the extreme case the impact of the internal valve seat can result in a shearing off of the sealing material on the sealing cup.
Therefore, the object of the present invention is to further improve a generic pre-controlled valve to the effect that the sealing cup, used in connection with the valve seat assembly, makes it possible to decrease the internal diameter of the valve seat in order to increase the force component above the sealing cup and simultaneously ensures a reliable sealing function during continuous operation.
The problem is solved, according to the invention, starting from a precontrolled valve comprising a valve housing containing an axially adjustable control piston which can be actuated by at least one electromagnetic pilot valve, and which actuates a valve seat assembly to switch compressed air flow between at least one external brake line connection, a feed pressure connection, and a venting port, wherein the valve seat assembly includes a pot-like sealing cup with a coaxial passage. The sealing cup includes an internal reinforcing insert, which is formed essentially in the shape of a U according to the cross section of the edge and which is provided with a molded-on shoulder, which is oriented radially towards the inside and reinforces the inside radial area of the sealing area, whereby the two legs of the reinforcing insert project reinforcingly into the respectively assigned sealing lip segments of the sealing cup.
An advantage of such a designed sealing cup lies in the fact that the critical area of the sealing area that corresponds with the internal valve seat is supported in such a manner by an especially facilitating geometry of the reinforcing insert that the diameter of the valve seat can be reduced even further in order to enlarge in this respect the effective ring area above the sealing cup without impeding the axial moveability of the sealing cup. As a consequence, a smaller valve hysteresis is achieved, a feature that results in a better control quality of an electropneumatic regulating valve.
Preferably the reinforcing insert is made of a relatively rigid plastic, as compared to the enveloping elastomeric sealing material of the sealing cup, and which is vulcanized into the sealing cup. In addition, it is also conceivable to use a reinforcing insert made of steel, aluminum, or the like.
According to another embodiment of the invention, the two ring-shaped sealing lip segments, issuing from the sealing lip cup, are designed approximately the same length in order to guarantee a uniform quality of sealing in interaction with the legs of the reinforcing insert, said legs being also of equal length, without the different contact forces on the housing components, which correspond to the sealing cup, resulting in the axial moveability of the sealing cup being impeded.
According to a further embodiment of the invention, a tube segment with a venting duct can be run through the passage in the sealing cup, in order to guide the exhaust air, accumulated while venting the control chamber, directly into the area of the venting port. Correspondingly the diameter of the passage is matched with the diameter of the tube segment in such a manner that a circular ring-shaped flow cross section, which is just adequate enough to vent the working chamber.
Other objects, advantages and novel features of the present invention will become apparent from the following detailed description of the invention when considered in conjunction with the accompanying drawings.